Smoke being generated blocky
I also have this problem regularly and i figured out this is because of low Resolution , you need to increase Resolution Divisions of your domain to something like 400 or 500 for good results but WARNING if you are working on a low spec device like a normal consumer laptop , Even with 4 gb or 8bg ram this could be problematic but if you have a good build with some OKAY graphics , 500 divisions should not be a problem but on a simple laptop Blender will HANG as hell of you even crank up to 200